Potential of zygotes to produce live births can be identified by the size of the male and female pronuclei just before their membranes break down.

The birth of healthy babies resulted from zygotes that contained pronuclei of similar size when the measurements were made immediately before the PNMBD. Evaluating the size of each pronucleus immediately before the PNMBD provides an effective indicator of the embryo's potential at an early stage of development.